This invention relates to an adjusting device for a color cathode ray tube, and more particularly to such a device for adjusting the static convergence and color purity of electron beams in a color cathode ray tube.
As well known, the front panel of color cathode ray tubes has a multiplicity of phosphor dots for each of three primary color located on the internal surface thereof at positions where electrons of an electron beam from an associated electron gun land successively after having passed through a shadow mask disposed adjacent to the internal surface of the front panel. However, those electrons may not actually land at their assigned phosphor dots for various reasons and principally due to deviations of mounting positions and directions of the electron guns and those of relative positions and directions therebetween. More specifically, upon manufacturing color cathode ray tubes, one first presumes positions and directions of the triad of electron guns for the respective primary colors disposed within the neck portions thereof and then applies phosphor dots or stripes for each of the primary colors to the internal surface of the front panel thereof on the basis of the presumed position and direction of an associated one of the electron guns. Thus, a phosphor screen is formed on the internal surface of the front panel. Subsequently, the three electron guns are put at their presumed position and in the presumed direction as accurately as possible within the neck portion. At that time, if the electron guns have the actual positions and directions more or less deviating from the presumed positions and directions thereof respectively, then electron beams from the electron guns pass through a few stages of electron lenses to be classified in positional and directional differences until each electron beam lands on a phosphor screen or stripes at positions far removed from their correct positions. This results in errors of the static convergence and color purity of the electron beams which may be called hereinafter a "color deviation or mislanding." Since glass forms the great part of the structural members located about the three electron guns, deviations inevitably occur between the presumed positions and directions and the actual positions and directions of the electron guns. Therefore the color deviation necessarily occurs.
In order to adjust static convergence and color purity errors of electron beams in color cathode ray tubes, it is required to exert magnetic fields having independent directions and strengths on the electron beams respectively and there has been already known an adjusting device formed of three pairs of annular permanent magnets disposed at predetermined equal intervals around the neck portion of color cathode ray tubes. Each pair of permanent magnets are operative to establish a dipole, a quadrupole or a sextupole magnetic field. Each pair of associated permanent magnets have been simultaneously rotated about the longitudinal axis of the neck portion to change the direction of the mating magnetic field and also a relative angle between those two permanent magnets has been changed to vary the strength of that magnetic field to thereby adjust electron beam paths and therefore the static convergence and color purity of electron beams. Then, the three pair of annular permanent magnets have been fixed in their changed positions.
Conventional adjusting devices such as above described have been disadvantageous in that (1) the adjustment consumes long time because the six annular permanent magnets are separately rotated to adjust electron beam paths and then fixed in their rotated positions, (2) because of the presence of the six permanent magnets, the adjusting devices are so large as to hamper the assembling of the deflecting device which is to be mounted to the color cathode ray tubes, and (3) the adjustment is required to be manually effected, resulting in the impossibility of effecting an automatic adjustment.
It is a general object of the present invention to eliminate the disadvantages of the prior art practice as described above.
It is an object of the present invention to provide a new and improved adjusting device for a color cathode ray tube capable of effecting the highly precise adjustment with a small-sized magnet and contributing to improvements in stabilization of the performance of the color cathode ray tube.
It is another object of the present invention to provide a new and improved adjusting device for a color cathode ray tube, permitting a deflection device to be easily disposed on and removed from the color cathode ray tube.
It is still another object to the present invention to provide a new and improved adjusting device for a color cathode ray tube readily changed into a magnetization pattern as required and permitting the adjusting operation to be automatically performed.